Sporogony of Theileria sergenti in the salivary glands of the tick vector Haemaphysalis longicornis.

Sporogony of Theileria sergenti in the salivary glands of the tick vector Haemaphysalis longicornis was observed by light and transmission electron microscopy. Fission bodies that developed from kinetes were observed as masses (approximately 32 x 15 microns) that occupied half of the acinous cell at 2 days after the infestation of ticks. Parasites possessed an irregular nucleus of low electron density, highly electron-dense granules, and mitochondrion-like bodies in the cytoplasm. Parasites developed into a multinucleate syncytium, increasing in size and complexity. Subsequently, the nuclei of parasites became round and highly electron-dense, and tubelike structures and rhoptries as precursors of the highly electron-dense granules appeared in the cytoplasm. Approximately 40,000 sporozoites arose via radial budding from the syncytium that had developed from kinetes. As in T. parva, no evidence of discrete secondary or tertiary sporoblasts was found in T. sergenti. The sporogony of T. sergenti was extremely similar to that of T. parva.